The present invention generally relates to a storage system, and in particular relates to a storage system in which an external storage is connected to a storage subsystem.
In order to deal with a system environment that changes suddenly due to the increase in the data amount or traffic volume, a storage subsystem loaded with a virtualization function is known. As a result of connecting an external storage to the storage subsystem, the storage subsystem is able to provide, based on this virtualization function, its own storage area and a storage area of the external storage as a single storage pool to a user through virtualization.
As conventionally technology related to this kind of storage subsystem, for instance, U.S. Pat. No. 7,111,138 describes a storage system in which a second storage subsystem is externally connected to a first storage subsystem. More specifically, the first storage subsystem comprises a virtual volume mapped with a real volume of the second storage system. The write data sent from a host apparatus to a virtual volume is transferred from the first storage subsystem to the second storage subsystem, and stored in the real volume mapped to the virtual volume.